Downshifting work vehicle using differential lock switch

Abstract

The differential lock switch for a work vehicle is used to trigger a control system for downshifting the vehicle from second to first. The control system comprises five relays. The first three relays detect if the vehicle is in second; if the vehicle is going forward; and if the differential lock switch is actuated. The fourth relay is used to latch the signal from the third relay so that the differential lock switch can be released and the vehicle will remain in first. The fifth relay receives signals from the first four relays and manipulates the correct solenoid valves for downshifting the vehicle.

We claim: 
     
       1. A self-propelled work vehicle for performing a work operation, the vehicle comprising: a supporting structure;   ground engaging wheels mounted to the support structure;   a prime mover supported by the supporting structure, the prime mover supplying power to the vehicle;   a transmission operatively coupled between the prime mover and the ground engaging wheels for propelling the vehicle, the transmission having at least two gear positions, the transmission is also provided with a lockable differential, the lockable differential having an actuation switch for locking the lockable differential; and   a control system for shifting the transmission from one gear to the other, the control system having a control switch that triggers the system and is interconnected with the differential lock switch, whereby actuation of the differential lock switch triggers the control system for shifting the transmission when the control switch is actuated.   
     
     
       2. A work vehicle as defined by claim 1 wherein the differential lock switch is non-latching. 
     
     
       3. A work vehicle as defined by claim 2 wherein the differential lock switch and the control system actuation switch are coupled in series. 
     
     
       4. A work vehicle as defined by claim 3 wherein the control system is provided with a gear sensor for detecting which of the two gears the transmission is operating, the gear sensor providing a gear signal. 
     
     
       5. A work vehicle as defined by claim 4 wherein the control system is provided with a direction sensor that detects which direction the vehicle is being driven, the direction sensor providing a direction signal. 
     
     
       6. A work vehicle as defined by claim 5 wherein the control system is provided with a switch sensor that detects of the differential lock switch and the control switch are actuated, the switch sensor providing a switch signal. 
     
     
       7. A work vehicle as defined by claim 6 wherein the control system is provided with a latching assembly for storing the switch signal from the switch sensor by latching the latching assembly. 
     
     
       8. A work vehicle as defined by claim 7 wherein the control system is provided with a downshift sensor for detecting the gear signal, the direction signal, and the switch signal, and the control system in response to these signals, shifts the transmission. 
     
     
       9. A work vehicle as defined by claim 5 wherein the gear sensor comprises a first relay and the direction sensor comprises a second relay, the first and second relays being coupled in series. 
     
     
       10. A work vehicle as defined by claim 9 wherein the switch sensor comprises a third relay and the latching assembly comprises a fourth relay, the third and fourth relays being coupled in parallel with the first and second relays. 
     
     
       11. A work vehicle as defined by claim 10 wherein the fourth relay is provided with a feedback loop for the gear signal and the direction signal, latching the fourth relay in response to the switch signal. 
     
     
       12. A work vehicle as defined by claim 11 wherein the downshift sensor comprises a fifth relay which is actuated by the gear signal, direction signal and switch signal. 
     
     
       13. A work vehicle as defined by claim 7 wherein the latching assembly becomes unlatched in response to the gear signal. 
     
     
       14. A work vehicle as defined by claim 7 wherein the latch assembly becomes unlatched in response to the direction signal.